This invention is directed to a seal for a pouch packaging machine. The seal includes first and second seal bars each having a sealing surface. The sealing surface of the two bars are asymmetrical with respect to one another.
Many commodities are packaged on form, fill and seal packaging machines. Packaging pouches are formed on the machines from rolls of polymeric or metallized films or combinations of the same. The pouches are filled, sealed and then disconnected from an advancing stream of the pouches for distribution and ultimately customer consumption.
Alternatively to separating the individual pouches formed on form, fill and seal pouch machines, the pouches are filled with a liquid and are maintained joined together in a checker board like matrix. These checker board like pouch matrices are commonly termed blankets. If a so-called blanket is cooled such that the liquid within its pouches or cells is frozen, the blanket can then be transferred to a container to cool the contents of that container. Further, such "cold blankets" can be used for medical purposes as cold compresses for treating sprains and other injuries. In a like manner a liquid filled blanket can be heated and used for transferring heat.
It is important in the above referenced liquid filled blankets that the individual pouches or cells of the blanket can be completely filled with liquid and be void of gas. Any gas within an individual cell or pouch of such a blanket is subject to large volume changes on cooling and heating. Such volume changes can lead to rupture and/or premature failure of an individual cell or pouch of such a blanket. If the cell or individual pouch is ruptured its liquid contents would be lost which, at the minimum, would compromise the efficiency of the blanket, or in its extreme, would render the blanket useless.
In forming one of the above referred to blankets on a form, fill and seal pouch packaging machine, the machine is equipped with a plurality of pairs of side seals. The individual members of the pairs of side seals come together to form a series of parallel tubes in the film or webbing being processed on the pouch machine. A first cross seal is formed to form a bottom in each of these tubes and liquid is then injected. Further cross seals must now be made through the liquid to form the cells of the blanket.
Seals are formed on form, fill and seal packaging machines by heating the individual films under pressure. The heat and pressure adhere one film to the other to form the seal. To assist in forming a seal, generally the films utilized for forming the pouches are multi-layered films specially constructed such that the inside layers will melt and/or flow together to join two films about a seal or seam. If liquid is present between the two films, the films will not adhere to one another and an ineffective and/or inefficient seal is formed. Thus, in forming any seal through a liquid, whether or not it be for the above referred blanket or for other pouch applications, it is necessary to remove the liquid from the surfaces of the films which are being sealed together.
Heretofore several expedients have been utilized to remove liquid from the surfaces of films which are being sealed together. These expedients rely on "squeegeeing" any liquid from the seal area prior to formation of the seal. Prior utilized techniques and/or apparatus to form seals through liquids have certain inherent drawbacks therein. These drawbacks include complex mechanisms which are subject to wear and breakdown, or the use of materials as, for instance, silicon rubber, which are poor heat conductors.
In a first prior art mechanism, opposing sets of rollers are utilized to squeeze liquid out between films in a "wringer" like manner. Aside from requiring complex mechanical actions, these roller like devices pressurize the individual cells of a blanket and when this pressure is released, the pressure can disrupt a freshly made seal.
A further type device utilizes a silicon rubber pad on one side of the seal and a sealing bar on the other. The sealing bar squeezes the films against the silicon rubber pad. Because the silicon pad is constantly being flexed and unflexed, wear can occur. Further, the silicon rubber pad is a less efficient heat transfer mechanism than a metal sealing bar and thus it is more difficult to evenly heat the films to an optimum sealing temperature. Further, if a flat surface is utilized on the sealing bar which mates against the silicon rubber pad, because the silicon rubber pad can locally deflect, it is possible to trap beads of liquid between the films along the area of the seal. This degrades the seal.